1963-1979 Corvette Differential Rebuild Procedure


April 25,2004
Revised October 26, 2005

1963-1979 Corvette Differential Rebuild Procedure

By Gary Ramadei

Tools Required:
1. Dial inch - pound torque wrench, 0-30 range- It's important to use this type of wrench for accuracy.
2. Torque wrench- 0-150 ft/lbs. I prefer the click type
3. 1" dial indicator with magnetic base
4. 0-1" micrometer and / or 0-6" dial caliper
5. Impact wrench
6. Bearing splitter
7. 20 ton press
8. Brass drifts
9. Hammers
10. Basic hand tools
11. 2-jaw gear puller
12. ¼ " NPT tap
13. 90* snap ring pliers

Starting Procedure
1. Remove differential from car
2. Clean off dirt/oil, grease before opening
3. Remove rear cover and drain old oil into container
4. Check old oil for metal particles using a magnet
5. For ease in disassembly, mount the differential to an engine stand by using the 3/8-16 tapped holes for the strut rod bracket.
6. If the same ring and pinion is going to be re-used check the backlash and pattern before removing or disturbing bearings, pinion or carrier. Make note of backlash and pattern for future reference.
7. Stamp the carrier bearing caps - Right & Left so they can be put back on their original sides. They are machined per side.
8. Remove Pinion yoke nut
9. Remove carrier bearing caps & bolts. Note the bolt head markings. 6 line minimum required (grade 8).
10. Use a box wrench on one of the ring gear bolts and rotate the pinion to move the carrier out of the housing. The carrier bearing shims are preloaded and will require some force to remove the carrier.
11. Keep the carrier bearing shims together per side. Place them with the respective bearing cap.
12. Clean the carrier in solvent to remove oil.
13. Use an old side yoke and side yoke bearings mounted in a bench vise to hold the carrier assembly.
14. Use a brass drift to drive the old pinion out. Hold the pinion face so it doesn't crash to the floor or make up a plate to bolt to the bearing cap holes to catch the pinion while driving out.
15. Clean parts in solvent.

Disassembly for inspection
1. After cleaning housing, drive out old pinion bearing races.
2. Drive out old side yoke needle bearings, Torrington #BH2212
3. Chase the bearing cap holes with a 7/16-14 tap.
4. Use a file to radius the housing edges to remove any burrs or sharp edge.
5. Optional but recommended. Drill and tap a drain hole for ¼" NPT. Locate at 1" from the edge of the strut rod bracket pad. Use of a magnetic plug is recommended. CAUTION: tapping a NPT plug requires you not to fully tap the hole. Continue to check the fit of the plug in the hole and stop when you have ½ the tapered thread screwed in. Over tapping the hole will result in a leak. Use Permatex high temp thread sealant on the plug threads when installed.
6. Check housing for any damage, cracks, etc. Note the side yoke holes to see if the yokes were worn to the point of grinding into the housing.
7. Remove the ring gear bolts from the gear/carrier. These should be tight, some of the later 70's differentials had a problem with loose ring gear bolts.
8. Using a mallet tap off the ring gear. Check for wear, chip teeth, cracks, etc.
9. If reusing the ring gear, stone down the backside where the bolt-holes are to remove any burrs/high spots. I recommend using new gears in most cases, the initial added cost may seem high but setting up unknown used gears or worn gears can be a hassle.
10. If using new gears, follow the same procedure for cleaning/deburring.
11. Mount carrier back on old side yoke in the bench vise so you can remove the posi clutches.
12. Use channel locks, bolt or tie together the posi springs. These are under pressure so be careful they don't fly out.
13. Remove the 7/16 hex head pinion gear "pin" bolt from the carrier, retain the star washer.
14. Slide out the pinion gear shaft or "pin" from the carrier.
15. Remove the posi spring plates.
16. Rotate the carrier on the yoke until one pinion gear and cup washer is in the large "window" and can be removed.
17. Rotate the carrier until the other pinion gear and cup washer can be removed. The upper side gear in the carrier will have to be supported by hand as the carrier is rotated to prevent it from falling down into the carrier.
18. With the pinion gears removed, remove the side gears, posi clutches, side gear shims, and clutch retainers.
19. Clean the parts again and keep the clutches with each side together.
20. Use a 2-jaw puller and remove the carrier bearing cones. A spacer the diameter of the carrier boss will be needed to press against when using the puller. Note: the boss is slightly higher then the bearing ID race. It is important the bearing ID race is fully seated against the shoulder of the carrier when installing new bearing cones.
21. Inspect the type of posi clutch and the condition. There are several types of clutches. Eaton used solid steel and "snowflake" steel clutches. The "snowflake" clutches are slotted to get oil in between the clutches to eliminate chatter when they are hot and the car is cornering. They didn't work too well. Eaton now sells carbon fiber clutches also. However, I was told they don't hold up to extreme usage. Regardless, I use the solid steel clutches still available from any Eaton dealer.
22. Inspect the clutch surface. They should have a solid diamond pattern to them. If they are shiny and the pattern is worn replace them. The new thickness of clutches is .068"-. 069" anything thinner then .067" I would replace the set. Most shops replace the clutch set as a normal rebuild procedure. The cost of a new set is about $100. It's not worth the trouble of having to remove the differential to replace them a short time later.
23. Optional, but Highly recommended: Polish the carrier housing once it is clean and stripped of parts. Radius the edges of all the non-machined surfaces. This removes high spots that could lead to cracks in the casting. I place the carrier in a lathe and polish it with 240 grit and then 400-grit emery cloth. A die grinder or Dremel tool with stone or rotary bit will radius the edges, but don't cut deep into the carrier, just round off the edges smooth.
24. Check for cracks from the window openings to the center pinhole. Check the pin hole for a step or egg shape. If worn badly then boring out a plug to the original dimension or bushing it can repair the carrier. Finding a good machine shop to align the bore may be a problem in some areas. Used Eaton carriers are now hard to find, you may have to buy a new loaded carrier. The pin should slide in the holes without any resistance but not be sloppy.
25. With respect to the new Eaton carriers, part number 19670-010 they come loaded with fiber clutches. Again I have never used these so I can't offer an opinion on life or torque range. One friend who used them had a problem with chatter, but I don't know who set them up so it could have been another issue related to them? I use only the solid steel Eaton clutches in my cars.
26. Inspect the carrier posi gears. There are a couple of different types depending on the year of the car. Count the number of teeth of both the side gear and pinion gear. They will be 10/16, 10/17, or 10/18. The 10/17's are the best and strongest. Treated 10/17 sets are available for HD.
27. The gears are ok to re-use as long as there is no damage to them.
28. If you are following the GM posi procedure, the side gear backlash will need to be measured. Shims are used behind the side gear to obtain the specified backlash per side. Once the backlash is correct the 4 springs can be installed. Follow the procedure in a GM overhaul manual to fully understand. I do not use this procedure. Instead I "tune" the posi.
29. Using a die grinder or Dremel tool, radius the edges of the side gear and pinion teeth. Just apply minor pressure to round off the edge not cut into the tooth.
30. OptionalPosi Tuning Procedure: purchase a shim kit. Start out using .045" shim behind each side gear. Assemble the carrier without the 4 posi springs or plates. Gather the posi clutches you will be using. Look at the edges of the clutches and you should see where the stamping was done and the grooves are deeper on one side. Sometimes a magnifying glass helps determine the side. Alternate stacking the clutches by the groove depth-deep side against shallow side, deep side, shallow side, etc. The clutches with tabs go in between the solid clutches and follows the same pattern with the grooves. Lube the clutch surfaces with GM posi additive as you assemble them. Use the retainers to hold the clutches together while installing them into the carrier. With the carrier assembled rotate it on the side yoke in the vise. It may be loose or snug. Flip the carrier over and check the other side gear for feel. If the gears are too loose add shims in .005" increments until the teeth of the side gear and pinion gears start to bind. I use a large spanner wrench to rotate the carrier on the yoke. When the gears start to bind remove .005" shim from the side gear you are checking. I remove the shim and grind it on a surface grinder once I get to the point of gear bind. I remove .001" at a time until the gears just start to rotate without any binding. Once you get both sides to this point the carrier is ready for the ring gear.
31. Rebuild kits come with new 7/16-20 bolts. However they are not the shouldered type of bolt the factory used. If you can find the original type use them. Another option is to use ARP #230-3001 ring gear bolts. They add about 430 to the job but are high quality bolts. Always install new bolts when installing the ring gear. Use red Loctite, #271 or #272 high temp, thread locker on the ring gear bolts. I cut the heads off the old bolts and slot them to use a screwdriver with. Screw a bolt into every other tapped hole in the ring gear. This will act as a guide to draw up the ring gear. Install the new bolts in the remaining open holes, using Loctite on them. I use an impact gun to slowly draw up the ring gear. You can also use a press but be careful not to damage the gear teeth. With the gear in place remove the screw in bolts and install the balance of new bolts again using the red Loctite. Torque in a star pattern to 55 ft/lbs.
32. Install new carrier bearings. Be sure they are seated against the hub shoulder. A large socket can be used to support the ID race while pressing the bearing on.
33. The carrier is now complete and read for installation in the housing. Put it aside until you are ready to use it.
34. Remove the old pinion bearing from the pinion. A bearing splitter and press will be needed to remove the bearing. Save and note the shim size under the bearing. This shim will determine the pinion depth into the ring gear. It is vital to get the pinion centered on the ring gear during setup or gear noise or damage will result.
35. Inspect the old pinion for wear or damage if reusing.
36. Setup Note: I use an old good bearing that I polished the ID on so it will slip fit onto the pinion. This will save pressing the new bearing on/off several times and remove the risk of damaging it.
37. Use the original shim or equivalent size in a new shim on the pinion to start.

Differential Assembly
1. Install the new pinion bearing races in the housing. I use a seal/race tool made out of aluminum. A brass drift or steel plate will also work.
2. Lightly oil the races with 90-wt-gear oil and install the pinion.
3. Holding the pinion in place against the race, install the yoke, washer, and original nut. Note: Do not use the new nut, seal, or crush sleeve at this time.
4. Tighten the nut until the bearings seat and removes end play. Using a dial in/lb. torque wrench with 0-30in/lb rating tighten the nut until there is 15-17 inch/lbs. of rotational drag on the bearings. This will preload them in the final position. A very slight tap with a brass hammer or drift against the pinion ends will help seat the bearings. Remember very light tap!
5. Install the carrier in the housing. Rotate the pinion by hand to be sure they move freely.
6. Using new shims add approximately the same size per side as the original cast shims were. Do not use the original cast shims. You may have to decrease the shim size to start.
7. The carrier should drop in with just a little resistance. It should be able to be removed by hand.
8. Install the bearing caps and torque to 60 ft/lbs. Do not use the bolts to draw down the caps, instead use a hammer to tap the caps in place then torque.
9. With the caps torqued check the backlash in the ring gear. Use a 1" dial indicator and magnetic base to check the backlash. Backlash ranges from .006-. 010" depending on the gear manufacturer. Refer to your note on the original backlash if reusing the gears. I set new Tom's US Gears to between .007-. 009" and get a nice pattern.
10. If the backlash is not where it should be then you have to adjust the carrier shims in or out. If the backlash is too tight then the ring gear has to move away from the pinion. Remove .005 from the left shim and add .005 to the right shim as a starting point. If the backlash is too loose then the ring gear needs to go into the pinion.
11. Once the backlash is correct you need to see where the pinion is n relation to the ring gear center. Use marking paste, either white or yellow, and paint the teeth-both sides, in 2 places. Paint several teeth in each area.
12. Use a rag rolled up to act as a brake and load up the pinion gear while rotating it several revolutions in each direction. I use a 9/16" box wrench I made up. I took a 9/16-combo wrench and cut off the open-end side. I welded the wrench to a long piece of 5/8" Cold Roll Steel. Husky makes a nice double box wrench that works well too. A pattern will form in the marking grease. Look to see if the pattern is the same length in the base of the tooth and the top of the tooth. The convex side of the tooth is called the drive side, the concave side of the tooth is called the coast side. The end of the tooth near the center of the ring gear is called the Toe. The end of the tooth near the OD of the ring gear is called the Heel.
13. The pinion shim must be adjusted to get the pattern centered on the tooth, regardless of where the pattern is in relation to the toe or heel. Once the pattern is centered, see where the pattern is for the toe and heel. Ideally they should be both centered on the tooth but this is not always possible. If the drive side is centered or to the toe that's ok. Under load it will spread out toward the heel. Performance setups are toward the Toe on the drive side. The coast side should be centered. With new gears and correct shim and backlash the pattern should be in this range. Refer to installation information that may come with the new gear set.
14. It will take several tries to get the pattern in range, so don't give up.
15. Decreasing Backlash moves the Drive side slightly lower and to the toe, the Coast moves lower and to the Toe.
16. Increasing Backlash moves the Drive side slightly higher and to the Heel, the Coast moves higher and to the Heel.
17. Thicker pinion shim with good Backlash moves the Drive side deeper and Slightly to the Toe. The coast moves deeper and more to the Heel.
18. Thinner pinion shim with good Backlash moves the Drive side to the top and to the Heel. The Coast moves tot he top and Slightly to the Toe.
19. Once the pinion shim, backlash, and pattern are correct then disassemble again.
20. Install the new bearing if you have been using a setup slip fit bearing. Setup again to get the pattern right.
21. With the correct pattern and new bearing installed, disassemble,
22. This time the crush sleeve or solid pinion shim will be installed along with a new pinion seal and new nut.
23. Oil the pinion bearing with 90 wt gear oil, install the pinion in the housing, install the crush sleeve and outer bearing, pinion seal, yoke, washer and new nut. Use Loctite red on the nut. Torque the nut to get your setup rotational drag. The trick here is the crushing of the sleeve. It will take a BIG impact gun, Long breaker bar, or some other device to start the crush. I have used two methods that work. The first one is to place the housing with the pinion, in a press and press against the pinion until the bearings seat. Then just a little bit more. Remove the housing and check it with the dial torque wrench. Once the sleeve begins to crush the impact gun will drive it down. You don't want to over crush the sleeve. If you over crush it then replace it with a new sleeve. The second method is to crush the sleeve in a press before installing it on the pinion. I measure the old sleeve to get a close reference point. Then install the sleeve in the press and use a plate against the OD. I press it until it starts to compress and begin the crush. I then install in on the pinion and use my impact gun to set it. Another method is to use a solid spacer and shims. This replaces crushing the sleeve, instead shims are used to set the length needed to preload the bearings and keep them from loosening up. I have not used the solid spacer yet but other have and report it is much faster and more accurate to set then the crush sleeve. The solid spacers can be made or purchased from Ratech in OH.
24. NOTE: The pinion seal Flange does not bottom out against the housing when installing. There should be a 1/8"(.125") gap between the housing and the seal flange. Use Permatex #2 sealant on the pinion splines to prevent oil leaking past the nut, I also put a little #2 on the seal OD Evenly tap the seal into the housing. A plate or wood block covering the seal OD will work to drive it in place. Place a little grease on the seal ID to prevent any dry damage when installing the pinion.
25. Install the carrier, only this time add .005 shim to each side to add a preload to the carrier bearings. You will have to hammer the shims in because of the increased thickness.
26. Install the bearing caps and at this time I swap out the hex head bolts for 7/16-14 socket head caps screws. They are a littler stronger. Some of the earlier differentials used a 5 line bolt marking that would not be a grade 8 bolt. The socket head cap screws are rated higher then grade 8 and work without any problem.
27. For HD applications a steel bearing cap and ½-13 bolts are used. This will require fitting of the cap and tapping the holes for the larger size bolts.
28. Install new Torrington BH2212 bearings in the side yoke bores, these are full needle bearings. Some of the kits I used came with bearings with half the needles in them. I trashed them.
29. Install new yoke seals. Some seals I've used are slightly larger OD and don't easily fit the bore. The CR seals that NAPA sells work very well if you find you need seals or the ones in the kit are NG.
30. Grease the seal ID here too.
31. Install the side yokes. I don't reuse side yokes. The originals were case hardened and ride up against the posi pin. The pin is harder and the yoke ends wear. Once the case hardening is gone they wear out quickly. It's best to replace the yokes during a rebuild. The exchange yokes sold are rebuilt using hardened tips to prevent wear and offer a very long life span.
32. With the yokes n place install new snap rings in the groove on the end of the yoke. You will need 90* snap ring pliers to install the rings. If you rebuilt the posi like I do then the end of the yoke will be right on the pin or within a few thousands. I fit a .001-. 004" gap in between them for oil to slip in. If you followed the GM overhaul manual you may have more end play in the yokes because the clutches will not be shimmed as close as the springless method.
33. Add two bottles of GM posi additive and 90-wt-gear oil.
34. Use Permatex #2 on the rear cover gasket and install the rear cover. Torque the bolts to 50 ft/lbs. I use the HD Muskegon Brake rear covers. They have thicker mounting tabs to withstand more abuse then the stock cover can. Also, improper rear spring installation can break the stock cover mounting tab off or crack the cover.

Break In Procedure:
1. If using a new ring & pinion gear set, drive the car for 10-12 miles moderately. Stop and let the differential cool for 45-60 minutes. Do this several times.
2. Drain the oil at 500 miles. Use new GM limited-slip additive and 90-wt oil.

PARTS:
I can supply you with all the parts in this procedure. I also make up POSI tuning kits with the solid steel clutches, new retainers, posi additive, full shim kit, pinion washers, and full instructions. Contact me at 203-776-2813 x139 days or 203-387-5374 evenings.

Notes:
I do not use synthetic oils or special additives. I use only the GM Limited-Slip additive and GM or equivalent 90-wt gear oil.

This procedure is the way I rebuild these differentials and is meant to be used as an educational tool for the corvette hobbyist. This procedure differs in some respect from the GM overhaul manual. I claim no responsibility for problems that may develop by individuals following this procedure. The end result of any mechanical repair lies in the hands of the mechanic performing the work. If you have any doubt of your skills or questions on this procedure, consider having a professional do the work.